Pusher units for use on vehicle conveyors of the type that contact a tire,.of a vehicle are shown in U.S. Pat. Nos. Re. 30,026 and 3,554,132. U.S. Pat. No. 4,374,496 is specially concerned with an improved pusher unit for use in such a system. Such three-axle, six-roller or "six-wheel" pushers have been widely adopted in the industry.
There exist problems with such prior three-axle pusher units. Such units are difficult and relatively expensive to make and difficult and time-consuming to install (often require shut-down and disassembly of the chain drive). There exists a problem with such units occasionally driving a vehicle wheel over the guide side rails and damaging the vehicle or the carwash equipment.
Further, the hollow ends of the rollers of such prior three-axle pushers which push against the tire, and to a lesser extent against the upper surface of the track, have, after an extended period of use, "crept" inward, binding up the roller, causing it to fail to turn.
This can result in the dragging of the tire against the non-rolling roller or on the track or both, increasing wear and increasing the energy needed to run the conveyor system.
Further, the rolling action between the tires and the rollers which contact the tires has tended to "grab" car wash brush fibers and break them off or pull them out of the brush units. This is a particularly vexing problem, as such brushes are relatively expensive, and the need to frequently replace them drives up the operating costs of the carwash.